JP2023074477A - Ridge filter in pbs treatment system and method for designing the same - Google Patents

Abstract

To provide a ridge filter in a PBS treatment system, and a method for designing the same.SOLUTION: A method for designing a ridge filter for a charged particle accelerator includes a step for dividing a cylindrical partial volume (Vi) that regulates a treatment volume (V) into N cells (Cij), and the ridge filter includes the same number of energy degrading units (11.i) as the number of existing spots (Si). The respective energy degrading units (11.i) are formed by N cylindrical degrading sub units unit (11.ij) with length (Lij) and area (Aij).SELECTED DRAWING: Figure 3a-3d

Description

The present invention provides a predetermined dose ( Dij) for a ridge filter. In particular, the invention relates to a method of designing such a ridge filter that optimizes the dimensions of such a ridge filter to accurately deliver dose (Dij) according to a pre-established treatment plan. The ridge filter of the present invention is particularly adapted for FLASH irradiation of the treatment volume (V) or portions thereof at very high dose delivery rates (HDR) with PBS.

Radiation therapy with particles or waves such as electron beams, proton beams, heavy ion beams, X-rays, γ-rays has become an indispensable tool for treating patients with tumors.

Since such radiation damages both tumor cells and healthy cells contained within the volume, tumor cells should be treated while limiting dose delivery to healthy cells so as to spare healthy cells as much as possible. A primary challenge in cancer treatment is to define a treatment regimen that ensures that a defined dose is delivered to tumor cells so as to effectively destroy or kill cancer cells. A second challenge is to actually deliver a defined dose to tumor cells while actually delivering a limited dose to healthy cells, especially healthy cells adjacent to the tumor cells.

The treatment plan must ensure that a total target dose sufficient to kill the tumor cells is delivered to the volume at the end of treatment while minimizing deterioration of healthy cells adjacent to the tumor cells. Different radiation will have different patterns of deposited energy. For example, X-rays impart most of their energy at depths near the skin, and the energy imparted decreases with depth of penetration into tissue. Thus, healthy tissue located upstream of the target volume of tumor cells receives a higher dose than tumor cells in the target volume. In contrast, as shown in FIGS. 2(a) and 2(b), charged particle beams, especially protons, impart most of their energy near the end of their beam path, the so-called Bragg form a peak.

Pencil beam scanning (PBS) is a technique consisting of steering a beam of charged particles along corresponding beam axes (Xi) towards individual spots of a mesh of spots (Sij) defining a target volume containing tumor cells. is. A predetermined target dose is thereby delivered to cells aligned in individual spots. The beam is steered along the corresponding beam axis (Xi) and dose delivery defines the dose (Dij) to be delivered to each cell aligned with a given spot along the beam axis (Xi). The scanning sequence of planning and spot exposure is followed. PBS reduces unnecessary radiation exposure of surrounding non-cancerous cells by shaping the area to be treated to mirror the geometry of the tumor. In addition to target geometry, the PBS allows local adjustment of the intensity of the beam depending on the position of the spot within the target.

The mesh generally includes several painting layers (Tj=T1-TN) perpendicular to the illumination axis (X) centered on the beam axis (Xi). On the corresponding upstream plane of each layer (Tj), spots (Sij, Si(j+1)...) are arranged in a two-dimensional array. Each painting layer has a number of cells (Cij, C(i+1)j . …). The cells (Cij) have the same thickness as the corresponding layers (Tj). The superposition of the painting layers (Tj) defines the entire treatment volume (V). The spots (Sij) in the upstream layer (Tj) are the corresponding spots (Si(j+1), Si(j+2)...) in the downstream layers (T(j+1), T(j+2)...). is not necessarily aligned along the beam axis (Xi) corresponding to .

The terms "upstream" and "downstream" are defined with respect to the direction of the beam of charged particles (100.i). As used herein, unless otherwise indicated, "generalized cylinder", "cylinder" and derivatives thereof refer to all cylinders passing through the perimeter of the base contained in planes parallel to and not parallel to the generatrix. Refers to the surface consisting of all points on a line. The bottom surface can have any flat geometric shape. Especially if the base is circular, it defines a cylinder. If the base is polygonal, it forms a prism. A right cylinder is a cylinder whose base is perpendicular to the generatrices.

PBS is extremely advantageous because it optimizes the geometric distribution of dose delivery to match the geometry of the treatment volume (V) surrounding the tumor. However, PBS can be time consuming because the beam must scan each spot (Sij) and each layer (Tj). It takes several ms to move the beam from one beam axis (Xi) to another beam axis (X(i+1)). Varying the energy of a given beam parallel to a given beam axis (Xi) to deliver a desired dose (Dij) to cells (Cij) of different layers (Tj) is more time consuming. , on the order of 500 milliseconds. Therefore, the number of layers (Tj) strongly influences the duration of treatment.

With an accelerated proton beam, a given beam parallel to a given beam axis (Xi) produces several Bragg peaks with offset depths in each painting layer along the beam axis (Xi). The superimposition allows a given charge to be applied one after the other to corresponding cells (Cij) of each painting layer aligned along a given beam axis (Xi). This results in an expanded Bragg peak (SOBP) over all cells (Cij, Ci(j+1)...) aligned along a given beam axis (Xi). However, this operation requires successively changing the energy of a given beam such that the corresponding Bragg peak is centered on the corresponding cell (Cij). This operation is time consuming. Like painting, painting several layers or changing the energy of a given beam from time to time is time consuming. With one fixed energy beam, i.e. by applying a single paint layer, all doses (Dij ) can be given.

Reducing treatment time reduces the time each patient occupies the particle accelerator. It is also more comfortable for the patient. It is also advantageous if the treatment regimen includes FLASH radiation delivered to the cells at a very high dose delivery rate (HDR) with a dose of at least 1 Gy/s. A given dose delivered at HDR has been found to spare healthy cells compared to the same dose delivered at a low delivery rate (LDR). Of particular interest to FLASH irradiation is that a given dose delivered to tumor cells has the same killing effect whether delivered HDR or LDR. However, the layer-by-layer application of the dose (Dij) to the treatment volume (V) by the PBS causes all cells (Cij) aligned along a given beam axis (Xi) to receive the corresponding dose (Dij). , cells located upstream in the volume (V) are necessarily repeatedly irradiated multiple times, resulting in a significantly lower delivery rate to the cell.

Delivery of a given dose (Dij) to the treatment volume with PBS in a single layer can be achieved by using a ridge filter. Using a ridge filter requires that the spots (Sij, Si(j+1)...) in each layer (Tj) be aligned along the corresponding beam axis (Xi). Ridge filters with energy degrading units in the form of flat-surfaced pyramids or stepped pyramids or ridges have been shown in the art. For example, [1] describes a ridge filter comprising a plurality of energy degrading units in the form of flat-faced pyramids extending along the beam axis (Xi) corresponding to each spot (Sij). there is [2] describes a multi-layered ridge filter, the layers overlapping each other, each layer comprising parallel linear ridges with stepped pyramidal cross-sections. WO 2005/010000 discloses a conical or triangular-pyramidal filter placed upstream of a plate-shaped Bragg peak broadening filter with a plurality of through-holes for widening the SOBP along the corresponding beam axis (Xi). describes a ridge filter with protrusions of .

The principle of a ridge filter is that portions of a beam (100.i) of given energy directed along the corresponding beam axis (Xi) pass through different material thicknesses of the filter and have different ranges. From the spot (Si1) in the first layer (T1) across the depth of the treatment volume (V) along the corresponding beam axis (Xi) by generating Bragg peaks and superimposing them to: A uniform SOBP is obtained over the cylindrical volume defined by the corresponding spot (SiN) in the last layer (TN) downstream of the first layer (T1).

であり、ここで、Ｂ（ｚ）は、測定される元のブラッグピークであり、Δｚは、連続するブラッグピーク間のステップサイズであり、重みωｉは、各ピークｉのＳＯＢＰへの寄与度を決定し、Ｄ（ｚ）は、結果として得られる深さ線量分布である。この式を解くには、実験的に当てはめられる関数が必要となる。（非特許文献２）は、そのリッジフィルタをどのように設計するかについて、モンテカルロ計算が使用されていること以外、あまり情報を提供していない。 Designing and dimensioning the energy degrading unit of a ridge filter remains a challenge. (Non-Patent Document 1) describe a complex method for dimensioning the pyramidal protrusions forming the ridge filter, which involves minimizing the function (DSOBP-D(z)) ² , DSOBP specifies a uniform dose distribution,

where B(z) is the original Bragg peak to be measured, Δz is the step size between successive Bragg peaks, and the weight ωi measures the contribution of each peak i to the SOBP and D(z) is the resulting depth dose distribution. Solving this equation requires an experimentally fitted function. [2] does not provide much information on how to design the ridge filter, other than that Monte Carlo calculations are used.

JP 2019-136167 A

Simeonov et al. , Phys. Med. Biol. 62 (2017) 7075 Sakae et al. , Med. Phys. 27, 2, (2000) 368

Therefore, there is a need for a simple, reliable and reproducible method for dimensioning the energy degrading unit of a ridge filter. An alternative ridge filter design is proposed that is easier to manufacture to the required precision. These and other advantages are described in more detail below.

The present invention provides a charged particle accelerator (preferably a proton accelerator) for delivering a specific dose (Dij) to a specific location within a treatment volume of tissue containing tumor cells using a beam of accelerated particles; It relates to a method of designing ridge filters for treatment systems including beamline nozzles, collimators, etc. (collectively referred to herein as accelerators). The present invention relates to dosing by spot-by-spot pencil beam scanning (PBS) according to a predetermined treatment plan (TP) in a single painting layer defining the entire treatment volume. The beams extend along corresponding beam axes (Xi) that are substantially parallel to the irradiation axis (X) and deviate from parallel to the irradiation axis (X) by an angle within ±5°, preferably within ±3°. Tissue is characterized by a maximum beam range (W0) defined as the water equivalent distance at which the beam no longer propagates through the tissue. The method includes the following steps.

The expression "water equivalent thickness" (=WET) is well-known in the art and refers to the amount of water that causes the same energy degradation of the particle beam as a given thickness of material or materials traversed by the particle beam. Defined as thickness.

The inscribed boundary of the treatment volume is defined by defining the area (Aj) over the upstream plane (Y,Z)j of N slices (Tj=T1-TN) of thickness (dxj). The plane (Y,Z)j is perpendicular to the illumination axis (X). The shortest water equivalent thickness (d0) and the longest water equivalent thickness (d1) for the patient's skin are the boundary points closest to and farthest from the skin measured along the illumination axis (X). are respectively defined as

An array of sub-volumes (Vi) is defined, each sub-volume extending parallel to the corresponding beam axis (Xi) from the patient's skin to the corresponding furthest water equivalent thickness and in a plane perpendicular to the irradiation axis (X) ( The projection of the array of partial volumes (Vi) onto the plane (Y,Z) defines an array of spots covering the entire area of the projection of the volume onto the plane (Y,Z).

For each slice (Tj) of the N slices (T1-TN) contained within the subvolume (Vi), a cell is defined as a portion of the subvolume (Vi) contained within the corresponding slice (Tj) . For each cell of a given partial volume (Vi), the water equivalent thickness of the cell is determined from the skin to the geometric center of the cell. The beam weights (ωij) required to deliver a particular dose (Dij) to the cell according to TP are determined for each cell. The beam weights (ωij) are proportional to the number of charged particles in the water equivalent thickness of the cell.

A ridge filter is designed with a set of energy degrading units, each energy degrading unit applying a specific dose (Dij) to the corresponding cell contained within a subvolume (Vi) according to TP. The initial energy (E0) of the beam of charged particles of a given beam diameter, coaxial with the corresponding beam axis (Xi) and subvolume (Vi), as given at the equivalent thickness, is reduced to the reduced energy ( Eij). An energy degrading unit for a given partial volume (Vi) is designed as follows.

For each cell of subvolume (Vi), a generalized cylinder with a base of area (Aij) perpendicular to the corresponding beam axis (Xi) and a generatrix of length (Lij) parallel to the corresponding beam axis (Xi) A degrading subunit having a geometry is dimensioned. The degrading subunits are made of a material that has a water equivalent thickness (Wu) of subunits per unit length along the corresponding beam axis (Xi) and the length is such that the degrading subunits have a unit length It is determined to have the water equivalent thickness of the subunit (Wij=Wu*Lij) equal to the product of the water equivalent thickness (Wu) and the length (Lij) of the per subunit. The sum of the subunit water equivalent thickness (Wij) and the cell water equivalent thickness (dij) is equal to the maximum beam range (W0) (ie, W0=Wij+dij).

As defined herein, "generalized cylinder," "cylinder," and derivatives thereof, refer to all cylinders passing through the perimeter of the base contained in planes parallel to and not parallel to the generatrix. Refers to the surface consisting of all points on a line. The bottom surface can have any flat geometric shape. Especially if the base is circular, it defines a cylinder. If the base is polygonal, it forms a prism. A right cylinder is a cylinder whose base is perpendicular to the generatrices.

ここで、フルエンスＦ（ｙ，ｚ）は、ビームの位置（ｙ，ｚ）におけるビーム（１００．ｉ）の単位面積あたりの電荷の数であり、底面面積（Ａｂｉ）は、サブユニットの面積（Ａｉｊ）の和に等しい（すなわちＡｂｉ＝Σ_ｊＡｉｊ）。 The degrading subunit area (Aij) is the degrading of the normalized beam weight (ωij/ _Σjωij ) of the integral of the fluence (F(y,z)) over the subunit base area (Aij). determined by equaling the ratio for the same integral over the base area (Abi) of unit (11.i),

where the fluence F(y,z) is the number of charges per unit area of the beam (100.i) at the beam position (y,z) and the base area (Abi) is the area of the subunit ( Aij) (ie, Abi=Σ _j Aij).

The N degrading subunits are combined to obtain an energy degrading unit designed to degrade the energy of the beam so as to impart the required dose (Dij) to the subvolume (Vi). Energy degrading units corresponding to all remaining partial volumes (Vi) can be designed as defined above.

In a preferred embodiment, a specific dose (Dij) is delivered according to a treatment plan at a very high dose delivery rate (HDR) to at least specific selected locations within the volume of tissue. Ultra high dose rate (HDR) is defined as a dose rate HDR≧1 Gy/s.

The spots of the array of spots should be no more than 1.8 times the standard deviation (σ) of the fluence (Fi(y,z)) of the beam in one single spot (ie ds ≤ 1.8σ), preferably 1.8σ. They may be separated from each other by a distance (ds) of 5σ or less. Under these conditions, the fluence (F(y,z)) of the beam passing through the base area (Abi) appears to be constant over all values of the plane (Y,Z)j defining the inscribed boundary of the volume. is approximated by

であるように近似され、ここで、（ｙｉ，ｚｉ）は、（Ｙ，Ｚ）平面における、スポット（Ｓｉ）のフルエンスの最大値（Ａｉ）の位置の座標であり、円形スポットの場合、σ_ｙ＝σ_ｚ＝σである。 Alternatively, the spots in the array of spots are more than 1.2 times the standard deviation (σ) of the beam fluence (Fi(y,z)) in a single spot (i.e. ds>1.2σ), preferably 1 They can be separated from each other by more than 0.5 times the distance (ds). Under these conditions, the beam fluence (Fi(y,z)) passing through the base area (Abi) has a Gaussian distribution

where (yi,zi) are the coordinates of the position of the maximum fluence (Ai) of the spot (Si) in the (Y,Z) plane, and for a circular spot, σ _y = σ _z = σ.

In a preferred configuration of the invention, the energy degrading unit is in the form of orifices arranged side by side according to the array of spots in the supporting base of thickness (Bi) measured along the beam axis (Xi). Each orifice extends from an opening that opens into the surface of the support base and penetrates to a given depth measured along the corresponding beam axis (Xi). Each energy degrading unit (11.i) has a generalized cylindrical geometry of cross-sectional area (Ai) and from the opening of the support block along the corresponding beam axis (Xi), with Lij=Bi−Lsij It is formed by one or more degrading subunits in the form of orifices extending over some length (Lsij). The degrading subunits defined above are located within the base area (Abi).

In the energy degrading unit of this configuration, at least two subunits can be arranged in any one of a series structure, a parallel structure and a mixed structure within the base area (Abi).

In a serial configuration, the degrading subunits are arranged along the corresponding beam axis (Xi) in order of decreasing length (Lsij), preferably coaxially, and the orifice with the longest length (Lsi3) is centrally located. aligned so that the The subunit base area (Aij) of a given degrading subunit is the sum of the cross-sectional area of the given degrading unit (Axij) and the cross-sectional area of the degrading unit circumscribed within the given degrading unit (Axi (j+1)) is equal to the difference in cross-sectional area (Axij-Axi(j+1)).

In a side-by-side configuration, the degrading subunits are arranged side by side in a base area (Abi) with either no space between two degrading subunits or space between two adjacent degrading subunits. be done.

In a mixed both parallel and series structure, three or more degrading subunits are arranged both in series and in parallel. The one or more structures are formed by two or more degrading subunits aligned in series along corresponding beam axes (Xi), and optionally one or more individual degrading subunits The units are arranged side by side within a base area (Abi).

In an alternative preferred arrangement of the invention, the energy degrading units are arranged side by side according to the array of spots and are supported on a support base of thickness (Bi) measured along the beam axis (Xi). is in the form of Each pin extends from the support base along a corresponding beam axis (Xi). In this configuration, each energy degrading unit has a generalized cylindrical geometry of cross-sectional area (Aij) and a length ( Lsij), formed by one or more degrading subunits. These degrading subunits are arranged within the base area (Abi).

In the energy degrading unit of this configuration, at least two subunits can be arranged in any one of a series structure, a parallel structure and a mixed structure within the base area (Abi).

In a serial configuration, the degrading subunits are arranged along the corresponding beam axis (Xi) in order of decreasing length (Lsij), preferably coaxially, with the pin having the longest length (Lsi1) at the central position. aligned so that the The subunit base area (Aij) of a given degrading subunit is the sum of the cross-sectional area of the given degrading unit (Axij) and the cross-sectional area of the degrading unit circumscribed within the given degrading unit (Axi (j-1)) is equal to the difference in cross-sectional area (Axij-Axi(j-1)).

In a mixed both parallel and series structure, three or more degrading subunits are arranged both in series and in parallel. The one or more structures are formed by two or more degrading subunits aligned in series along corresponding beam axes (Xi), and optionally one or more individual degrading subunits The units are arranged side by side within a base area (Abi).

In a preferred embodiment, at least the first degrading subunit of the first energy degrading unit is the second of the second degrading subunit of the first energy degrading unit or the second energy degrading unit It can be made of a first material different from the material. The first material, for example, changes the value of the length of the first degrading subunit (L11=W11/Wu) compared to the length of the corresponding first energy subunit made from the second material. It has a different water equivalent thickness (Wu) value of the subunits per unit length than the second material so as to increase, preferably decrease. By using different materials with different values of water equivalent thickness (Wu) of the subunits per unit length, the length of the first degrading subunit (L11) can be adjusted to make the energy degrading unit more compact. To do so, it can be kept within ±20% of the length of the second degrading subunit (Lij). The lengths (Lij) of all degrading subunits of the energy degrading unit preferably have the same length (Lij) within ±20% variation of the average length (Lm,ij) (i.e. Lij = Lm,ij±20%∀j).

FIG. 1(a) schematically shows the treatment volume (V). The treatment volume (V) is divided into sub-volumes (Vi) extending parallel to the corresponding beam axis (Xi) and each sub-volume (Vi) is divided into cells (Cij) in which cells (Cij) have a predetermined Dose (Dij) is given. The corresponding SOBPs are shown along different beam axes (Xi) passing through the corresponding energy degrading units of the ridge filter. FIG. 1(b) shows the treatment of FIG. 1(a) with SOBP obtained by three beams (100.i, 100.k, 100.m) after passing through the ridge filter according to the invention. Fig. 3 shows a side view of volume (V); FIG. 1(c) shows the SOBP obtained with the beam (100.i) extending along a beam axis (Xi) coaxial with the illumination axis (X). FIG. 1(d) shows the SOBP obtained with the beam (100.m) extending along the beam axis (Xm). FIG. 2(a) shows a typical Bragg peak depth-dose profile for a beam of given energy. The horizontal axis represents depth in water. The maximum beam range (W0) in water is the depth above the maximum Bragg peak and corresponding to an energy equal to 80% of the maximum Bragg peak, and W0 must be at least dij (dij<W0). FIG. 2(b) shows the depth dose profile of the Bragg peak of the beam of FIG. 2(a) with the energy degrading unit intersecting the path of the beam. FIG. 3(a) shows the beams (100.i, 100.i, 100.i) extending along their respective beam axes (Xi, X(i+1)...) parallel to each other and to the illumination axis (X) and passing through the ridge filters. (i+1)...). FIG. 3(b) shows the beams (100.i) fanning out about the illumination axis (X) and extending along their respective beam axes (Xi, X(i+1)...) and passing through the ridge filter. , 100.(i+1)...). FIG. 3(c) schematically shows a ridge filter with energy degrading units in the form of pins. FIG. 3(d) shows two energy degradings with beams (100.i, 100.(i+1)) extending along respective beam axes (Xi, X(i+1)) that are not parallel to each other. Units are shown (the angle between Xi and X(i+1) is exaggerated). FIG. 3(e) shows a volume element of a treatment volume (V) extending parallel to the irradiation axis (X) and comprising several sub-volumes (Vi) divided into cells (Cij). The SOBP obtained in partial volume (V5) is also shown. FIG. 3(f) shows the volume elements of the treatment volume (V) comprising several sub-volumes (Vi) extending parallel to the corresponding beam axis (Xi). The beam axes (Xi) are neither perfectly parallel to each other nor perfectly parallel to the illumination axis (X). The angular deviation is exaggerated for clarity. FIG. 4(a) shows an embodiment of a ridge filter with energy degrading units formed by gaps. FIG. 4(b) shows a cutaway side view of the gap forming energy degrading unit of the ridge filter of FIG. 4(a), composed of three degrading subunits. Also shown is the SOBP depth dose profile produced by the degrading unit. FIG. 4(c) shows a cutaway side view of the first degrading subunit of the energy degrading unit of FIG. 4(b). Two examples of possible cross-sectional shapes for the first degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the first degrading subunit is maximum at depth di1. FIG. 4(d) shows a cutaway side view of the second degrading subunit of the energy degrading unit of FIG. 4(b). Two examples of possible cross-sectional shapes for the second degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the second degrading subunit is maximum at depth di2. FIG. 4(e) shows a cutaway side view of the third degrading subunit of the energy degrading unit of FIG. 4(b). Two examples of possible cross-sectional shapes for the third degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the third degrading subunit is maximum at depth di3. FIG. 4(f) shows an alternative embodiment of a ridge filter with energy degrading units formed by gaps. FIG. 4(g) shows a cutaway side view of the gap forming energy degrading unit of the ridge filter of FIG. 4(f), composed of three degrading subunits. Also shown is the SOBP depth dose profile produced by the degrading unit. FIG. 4(h) shows a cutaway side view of the first degrading subunit of the energy degrading unit of FIG. 4(g). Examples of possible cross-sectional shapes for the first degrading subunit are shown. The Bragg peak produced by the first degrading subunit is maximum at depth di1. FIG. 4(i) shows a cutaway side view of the second degrading subunit of the energy degrading unit of FIG. 4(g). Two examples of possible cross-sectional shapes for the second degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the second degrading subunit is maximum at depth di2. FIG. 4(j) shows a cutaway side view of the third degrading subunit of the energy degrading unit of FIG. 4(g). Examples of possible cross-sectional shapes for the third degrading subunit are shown. The Bragg peak produced by the third degrading subunit is maximum at depth di3. FIG. 5(a) shows an embodiment of a ridge filter with an energy degrading unit formed by protruding pins. FIG. 5(b) shows a cutaway side view of a protruding pin forming the energy degrading unit of the ridge filter of FIG. 5(a), composed of three degrading subunits. Depth dose profiles of SOBP produced by the degrading unit are shown. FIG. 5(c) shows a cutaway side view of the first degrading subunit of the energy degrading unit of FIG. 5(b). Two examples of possible cross-sectional shapes for the first degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the first degrading subunit is maximum at depth di3. FIG. 5(d) shows a cutaway side view of the second degrading subunit of the energy degrading unit of FIG. 5(b). Two examples of possible cross-sectional shapes for the second degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the second degrading subunit is maximum at depth di2. FIG. 5(e) shows a cutaway side view of the third degrading subunit of the energy degrading unit of FIG. 5(b). Two examples of possible cross-sectional shapes for the third degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the third degrading subunit is maximum at depth di1. FIG. 5(f) shows an alternative embodiment of a ridge filter with energy degrading units formed by protruding pins. FIG. 5(g) shows a cutaway side view of the protruding pins forming the energy degrading unit of the ridge filter of FIG. 5(f), which is composed of three degrading subunits. Also shown is the SOBP depth dose profile produced by the degrading unit. FIG. 5(h) shows a cutaway side view of the first degrading subunit of the energy degrading unit of FIG. 5(g). Examples of possible cross-sectional shapes for the first degrading subunit are shown. The Bragg peak produced by the first degrading subunit is maximum at depth di3. FIG. 5(i) shows a cutaway side view of the second degrading subunit of the energy degrading unit of FIG. 5(g). Two examples of possible cross-sectional shapes for the second degrading subunit are shown: circular or polygonal (hexagonal). The Bragg peak produced by the second degrading subunit is maximum at depth di2. FIG. 5(j) shows a cutaway side view of the third degrading subunit of the energy degrading unit of FIG. 5(g). Examples of possible cross-sectional shapes for the third degrading subunit are shown. The Bragg peak produced by the third degrading subunit is maximum at depth di1. FIG. 6(a) is a cut side view of the energy degrading unit (11.i) of FIG. 4(b) comprising N=3 degrading subunits (11.ij) formed by continuous gaps. Figures and corresponding SOBPs are shown. FIG. 6(b) shows a variant of the energy degrading unit (11.i) of FIG. 6(a) and the corresponding SOBP, comprising N=6 degrading subunits (11.ij). FIG. 6(c) is the energy degrading unit of FIGS. 6(a) and 6(b) comprising N→∞ degrading subunits (11.ij) forming a continuous truncated generalized conical gap. Figure 3 shows a variant of (11.i) and the corresponding SOBP. FIG. 6(d) shows an energy degrading unit (11.i) comprising N=6 degrading subunits (11.ij) and the corresponding SOBP in the form of stepped pins. FIG. 6(e) is a variation of the energy degrading unit (11.i) of FIG. 6(d) with N→∞ degrading subunits (11.ij) forming a continuous truncated generalized cone. Morphology and corresponding SOBPs are shown. FIG. 7(a) shows the Bragg peak characterizing dose delivery by a beam passing through an energy degrading unit in the form of a protruding pin comprising two coaxially arranged degrading subunits of different length and cross-sectional area. indicates a shift. FIG. 7(b) shows the shift of the Bragg peak characterizing dose delivery by a beam passing through an energy degrading unit in the form of a gap comprising two degrading subunits with different lengths and cross-sectional areas. FIG. 7(c) shows the dose due to the beam passing through an energy degrading unit in the form of concentric elements comprising two degrading subunits with different densities and cross-sectional areas (the density of the inner element is lower than that of the surrounding elements). A shift in the Bragg peak characterizing the transfer is shown. FIG. 7(d) shows the dose due to the beam passing through an energy degrading unit in the form of concentric elements comprising two degrading subunits with different densities and cross-sectional areas (the density of the inner element is higher than that of the surrounding elements). A shift in the Bragg peak characterizing the transfer is shown. FIG. 7(e) Shifting of the Bragg peak characterizing dose delivery by a beam passing through an energy degrading unit in the form of a protruding pin comprising two side-by-side degrading subunits of different length and cross-sectional area. indicates Figure 7(f) shows a perspective view of an energy degrading unit (11.i) of the type shown in Figure 7(a). FIG. 7(g) shows a perspective view of an energy degrading unit (11.i) of the type shown in FIG. 7(e). FIG. 7(h) shows a perspective view of an embodiment of the energy degrading unit (11.i) comprising degrading subunits arranged in a mixed configuration of both serial and parallel configurations. Figure 7(i) shows a perspective view of an alternative embodiment of an energy degrading unit (11.i) comprising degrading subunits arranged in a mixed configuration of both serial and parallel configurations.

The present invention relates to a method for designing a ridge filter (11) for a charged particle accelerator, preferably a proton accelerator. The ridge filter (11) of the present invention uses a beam of accelerated particles (100.i), according to a predetermined treatment plan (TP), within a treatment volume (V) of tissue containing tumor cells (3t). It is configured to deliver a specific dose (Dij) to each spot (Si) of an array of spots by pencil beam scanning (PBS) at a specific location. By using a ridge filter, PBS can be performed with a single painting layer that defines the entire treatment volume (V). At the PBS, a narrow pencil beam is deflected to scan each spot (Si) in the array. Although it is a single beam that is deflected, in turn each beam (100.i) directed to a corresponding spot (Si) and extending along a corresponding beam axis (Xi) is directed to a different spot ( Sk, k≠i) and treated as individual beams distinct from the beam (100.k) extending along the second beam axis (Xk). As shown in FIGS. 1(b) and 3(a), the beam axis (Xi) is substantially parallel to the irradiation axis (X). In practice, the "individual" beams (100.i) are single beams deflected from a common accelerator exit point towards the individual spots (Si) of the array, so that the beam axis (Xi is within ±5°, preferably within ±3° from parallel to the irradiation axis (X), depending inter alia on the size of the treatment volume (V) and the distance of the exit of the accelerator from the treatment volume (V). Deviates at an included angle.

The tissue traversed by the beam (100.i) absorbs a portion of the beam's energy, which determines the penetration depth of the location of the Bragg peak along the beam axis (Xi). The penetration depth of the location of the Bragg peak in a given tissue is defined as the “water equivalent thickness” (=WET), i.e. the maximum beam range in water (W0 ) can be characterized by The expression “water equivalent thickness” (=WET) is well known in the art and refers to the amount of water that causes the same energy degradation of the particle beam as a given thickness of one or more materials traversed by the particle beam. Defined as thickness. Maximum beam range (W0) can be directly related to the depth of penetration of the same beam through tissue. Therefore, WET and penetration depth of the location of the Bragg peak through tissue can be used interchangeably, with the former (WET) being of course easier to test and measure experimentally.

A method for designing a ridge filter (11) according to the present invention comprises:
- defining a treatment volume (V) and a map showing locations and doses delivered to the treatment volume (V);
- Designing and dimensioning the ridge filter accordingly.

The definition of the treatment volume consists first of all of the boundaries inscribed in the treatment volume (V), as shown schematically in FIGS. including specifying This operation involves defining the area across the upstream plane (Y,Z)j of N slices (Tj=T1-TN) of thickness (dxj), where plane (Y,Z)j is the illumination axis perpendicular to (X). The upstream plane (Y,Z)j is the plane (Y,Z) of the slice (Tj) that the beam (100.i) first hits. The depth of the treatment volume (V) measured along the irradiation axis (X) is between the shortest water equivalent thickness (d0) and the longest water equivalent thickness (d1) measured from the patient's skin (3s). Included, these water equivalent thicknesses correspond respectively to the nearest and farthest boundary points to the skin (3s) measured along the illumination axis (X).

Second, as shown in FIGS. 1(a), 1(b), 3(e) and 3(f), the treatment volume (V) inscribed within the boundary is the subvolume (Vi) of Partitioned by defining an array. Each sub-volume extends from the patient's skin parallel to the corresponding beam axis (Xi) to the corresponding farthest water equivalent thickness (dl) and extends onto a plane (Y, Z) perpendicular to the irradiation axis (X). The projection of the array of volumes (Vi) defines an array of spots (Si) covering the entire area of the projection of the volume (V) onto the plane (Y, Z) (see Fig. 1(a) ).

Third, the partial volume (Vi) itself is divided into cells (Cij) as follows. For each slice (Tj) of the N slices (T1-TN) contained within the subvolume (Vi), a cell (Cij) as part of the subvolume (Vi) contained within the corresponding slice (Tj) Defined. This is illustrated in FIGS. 1(a), 3(e) and 3(f). For each cell (Cij) of a given partial volume (Vi), the water equivalent thickness (dij) of the cell from the skin (3s) to the geometric center of the cell (Cij) is determined. The beam weights (ωij) required to deliver a particular dose (Dij) to the cell (Cij) according to TP are determined for each cell (Cij). The beam weight (ωij) corresponds to the number of charged particles (eg, protons) delivered to the spot (Cij). The beam weights (ωij) are therefore proportional to the number of charged particles in the water-equivalent thickness (dij) of the cell.

Once the treatment volume has been divided into sub-volumes (Vi) and cells (Cij) and the beam weights (ωij) required to deliver a dose (Dij) to each cell (Cij) according to the treatment plan are determined, then The ridge filter (11) can be designed and dimensioned accordingly as follows.

A ridge filter (11) is applied to the corresponding beam (11) such that a particular dose (Dij) is delivered to the corresponding cell (Cij) contained within the sub-volume (Vi) according to TP at the water equivalent thickness (dij) of the cell. reducing the initial energy (E0) of a beam of charged particles (100.i) coaxial with the axis (Xi) and the partial volume (Vi) and having a beam diameter (D100.i) to a reduced energy (Eij) a set of energy degrading units (11.i) configured to: The principle is shown in FIGS. 2(a) and 2(b).

FIG. 2(a) plots the dose (Dij) delivered by a beam (100.i) of given energy (E0) along the beam axis (Xi) as a function of WET. As noted above, the maximum beam range (WET) in water is defined as W0, corresponding to a depth above the maximum of the Bragg peak and corresponding to an energy equal to 80% of the maximum of the Bragg peak. do. This means that a beam (100.i) of a given energy cannot penetrate tissue deeper than the corresponding water equivalent thickness W0 (ie d1≦W0). If d1>W0, ie if the treatment volume (V) extends deeper than the Bragg peak, a higher energy beam should be used. FIG. 2(b) shows the displacement of the Bragg peak when a degrading subunit (11.ij) is inserted in the path of the same beam (100.i) of given energy. In this case, it can be seen that the WET of the Bragg peak is at depth (dij<W0) from the skin (3s). This is because part of the energy (E0-Eij) of the beam (100.i) is absorbed by the degrading subunits (11.ij) through which the beam must pass. FIG. 2(b) shows how one Bragg peak forming WET=W0 can be displaced to the desired WET=dij by interposing a degrading subunit (11.ij). The SOBP is several Several degrading subunits (11.ij) can be superimposed to form an energy degrading unit (11i), each degrading subunit (11.ij) can be formed by superposing Bragg peaks. ij) are dimensioned to shift the Bragg peak from WET=W0 to the equivalent thickness of the corresponding cell (dij) and the required dose (Dij) is irradiated by beam (100.i) Ensure that each cell (Cij) of the volume (Vi) is attached. This is illustrated in FIGS. 6(a)-6(e), where N=3, N=6 and N→∞ respectively. Energy degrading units (11.i) composed of grading subunits (11.ij) and corresponding SOBPs are shown. The number of Bragg peaks and their corresponding cell water equivalent thicknesses (dij) required to obtain the desired SOBP according to TP must be determined. The number of Bragg peaks of a given beam (100.i) and thus the number of degrading subunits (11.ij) of the corresponding energy degrading unit (11.i) is equal to the number of slices (T1-TN) N . Each Bragg peak of a given beam (100.i) has a corresponding energy degrading unit (11.i) whose degrading subunits (11.ij) are arranged to obtain the required SOBP , and in turn can be designed to deliver the required dose (Dij) to the corresponding cell (Cij). In the case of N→∞ degrading subunits (11.ij) as shown in FIGS. Decreasing to zero, the surfaces of the truncated generalized cones shown in FIGS. can have a geometrically shaped bottom surface.

Each degrading subunit (11.ij) consists of a base of area (Aij) perpendicular to the corresponding beam axis (Xi) and a generatrix of length (Lij) parallel to the corresponding beam axis (Xi). has a generalized cylindrical geometry (ie not necessarily a cylinder). The degrading subunits shown in FIGS. 4(a)-4(e) and 5(a)-5(e) have circular or polygonal cross-sections. It is clear that other cross-sections are also possible. However, it is desirable to have some degree of symmetry in the cross section to facilitate the calculations that define the dimensions of the area (Aij). The degrading subunits are made of material that has a water equivalent thickness (Wu) of the subunit per unit length along the corresponding beam axis (Xi). The length (Lij) and area (Aij) of each degrading subunit (11.ij) can be dimensioned as follows.

と規定され、係数（Ｗ０－ｄｉｊ）は図２（ｂ）において図示されている。このようにして、ディグレーディングサブユニットの長さが完全に規定される。 The length (Lij) of a degrading subunit (11.ij) is the product of the subunit water equivalent thickness (Wu) and the length (Lij) per unit length of the degrading subunit (11.i). is determined to have the subunit water equivalent thickness (Wij=Wu*Lij) equal to . Considering that the sum of the subunit water equivalent thickness (Wij) and the cell water equivalent thickness (dij) must equal the maximum beam range (W0) (i.e., W0 = Wij + dij), the degrading subunit ( 11. The length (Lij) of ij) is

and the coefficient (W0-dij) is illustrated in FIG. 2(b). In this way the length of the degrading subunit is completely defined.

ここで、フルエンスＦ（ｙ，ｚ）は、ビームの位置（ｙ，ｚ）におけるビーム（１００．ｉ）の単位面積あたりの電荷の数であり、底面面積（Ａｂｉ）は、図４（ａ）及び図５（ａ）に示すようにサブユニットの面積（Ａｉｊ）の和に等しい（すなわちＡｂｉ＝Σ_ｊＡｉｊ）。図７（ａ）～図７（ｅ）に示すように、荷電粒子のビームのフルエンスは、一般にガウス分布を有する。ビームの直径（Ｄ１００）は、距離４σと規定され、σは、ビームのフルエンスを特徴付けるガウス分布の標準偏差である。スポットの陽子の約９５％がこの直径４σの中に位置している。 The area (Aij) of the degrading subunit (11.ij) is the normalized beam weight (ωij/ _Σjωij ) of the fluence (F(y,z)) over the subunit base area (Aij). determined by equaling the ratio of the integral to the integral of the fluence (F(y,z)) over the base area (Abi) of the degrading unit (11.i),

where the fluence F(y,z) is the number of charges per unit area of the beam (100.i) at the beam position (y,z) and the base area (Abi) is and equal to the sum of the subunit areas (Aij) as shown in FIG. 5(a) (ie, Abi=Σ _j Aij). As shown in FIGS. 7(a)-7(e), the fluence of the beam of charged particles generally has a Gaussian distribution. The beam diameter (D100) is defined as the distance 4σ, where σ is the standard deviation of the Gaussian distribution that characterizes the beam fluence. About 95% of the protons in the spot are located within this diameter 4σ.

4(b) to 4(e), 4(g) to 4(j), 5(b) to 5(e) and 5(g) to 5(j) In addition, the three degrading subunits (11.ij) of the energy degrading unit (11.i) are dimensioned and coaxially combined to produce the required dose (Dij ), an energy degrading unit (11.i) designed to degrade the energy of the beam (100.i) in order to impart .

The same operation is repeated to design energy degrading units (11.i) corresponding to all remaining partial volumes (Vi) as defined above.

Array of spots (Si) As shown in FIG. An array of spots (Si) covering the area is defined.

The oncologist characterizes the geometry and topography of the tumor area on the basis of images of the tumor area obtained by computed tomography (=CT scan). To reach the treatment volume (V), the beam (100.i) passes through healthy cells separating the treatment volume (V) from the patient's skin (3s), as shown in FIG. 1(b). This should irradiate both healthy and tumor cells. The oncologist defines a treatment plan that defines the dose (Dij) delivered to the treatment volume (V) and the dose delivery that should not be exceeded in healthy cells located outside (especially upstream) of the treatment volume .

The spot has a dimension perpendicular to the illumination axis (X), which can be equal to the beam diameter discussed above. The distance between adjacent spots, which defines the array density, is important because the higher the array density (i.e., the closer adjacent spots are to each other), the greater the effect of dose overlap on the spread cells of adjacent spots. is a parameter. Sufficient overlap is observed to confirm a uniform lateral dose distribution when the distance between adjacent spots is about 1.5σ.

In the first embodiment, the spots (Si) of the array of spots are not more than 1.8 times the standard deviation (σ) of the fluence (Fi (y, z)) of the beam (100.i) in a single spot (ie ds≦1.8σ), preferably separated from each other by a distance (ds) of 1.5σ or less. In this configuration, a given subvolume (Vi) is not only from beams (100.i) centered on the corresponding beam axis (Xi), but also from adjacent beams centered on adjacent beam axes. The fluence spreads over a given sub-volume (Vi) and also for a given degrading unit 11 . Receive a dose (Dij) spread over i. Considering the dose delivered to the subvolume (Vi) by adjacent beams, the fluence (F(y,z)) of the beam (100.i) passing through the base area (Abi) (see equation (1) ) is approximated to be constant over all values of the plane (Y,Z)j of the slice (Tj) defining the inscribed boundary of the volume (V).

であるように近似され、ここで、（ｙｉ，ｚｉ）は、（Ｙ，Ｚ）平面におけるスポット（Ｓｉ）のフルエンスの最大値（Ａｉ）の位置の座標であり、円形スポットの場合、σ_ｙ＝σ_ｚ＝σである。 In a second embodiment, the spots (Si) of the array of spots are the standard deviation (σ) of the fluence (Fi(y,z)) of the beam (100.i) at a single spot (100.i). separated from each other by a distance (ds) greater than 1.2 times (ie ds>1.2σ), preferably greater than 1.5 times. At such distances, the fluence of adjacent beams through a given degrading unit (11.i) can be neglected. Therefore, the fluence (Fi(y,z)) of the beam (100.i) passing through the base area (Abi) is Gaussian distributed

where (yi,zi) are the coordinates of the location of the maximum fluence (Ai) of the spot (Si) in the (Y,Z) plane, and for a circular spot, σ _y = σ _z = σ.

A dense array of spots (Si) may appear to always be advantageous over a less dense array. However, irradiating dense arrays increases the scan time required to cover the entire treatment volume (V). Furthermore, FLASH delivery, which delivers a dose (Dij) in HDR to obtain a FLASH effect for sparing healthy cells, results in longer delivery times (and correspondingly This is difficult to achieve in high density arrays because the rate of application slows down). Therefore, the density of the array of spots (Si) is determined individually.

Degrading unit (11.i)
The principle of the ridge filter (11) of the present invention is that for each spot (Si) a broadened peak is measured from the patient's skin (3s) so as to obtain the desired SOBP in the corresponding sub-volume (Vi) of the beam (100.i), bounded by a portion of the partial volume (Vi) extending between the shortest water equivalent thickness (d0) and the longest water equivalent thickness (d1) that is applied and contained within the treatment volume. It is to degrade the energy. The problem is to select a given beam out of the total weights (ωi) of the beams (100.i) such that the desired dose (Dij) is imparted to the corresponding cell (Cij) of the corresponding subvolume (Vi). It is to degrade the energy of a fraction of the beam (100.i) so as to move the Bragg peak of the weighted portion (ωij) to the water equivalent thickness (dij) of the corresponding cell.

To achieve the above objectives, here three geometrical shapes of the energy degrading unit (11i) are defined by the dimensions of the degrading subunits (11.ij) forming the energy degrading unit (11i): is proposed in conjunction with a corresponding method for determining One geometry can be combined with another to achieve the most convenient ridge filter.
an energy degrading unit (11.i) in the form of an orifice,
an energy degrading unit (11.i) in the form of a pin,
• An energy degrading unit (11i) combining different materials with different subunit water equivalent thicknesses (Wu) per unit length.

）ように構成される。 When the degrading unit (11.i) is an orifice, as shown in FIGS. 4(a) to 4(e), 4(f) to 4(j) and 6(a) to 6(c) In this embodiment, the energy degrading units (11.i) are arranged side by side according to the array of spots (Si) on a supporting base (11b) of thickness (Bi) measured along the beam axis (Xi). It is in the form of an orifice. Each orifice extends from an opening that opens into the surface of the support base (11b) and penetrates to a given depth measured along the corresponding beam axis (Xi). Each energy degrading unit (11.i) has a generalized cylindrical geometry of cross-sectional area (Axij) and from the opening of the support block (11b) along the corresponding beam axis (Xi), Lij = Bi - formed by one or more degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) in the form of orifices extending over a length (Lsij) such that Lsij. so that the degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) are within a diameter slightly greater than or equal to the diameter (D100) of the beam (100.i), and The sum of the subunit base areas (Aij) equals the base area (Abi) (i.e.

) is configured as

In the preferred embodiment shown in FIGS. 4(a)-4(e) and 7(b), the degrading subunits are arranged in a serial configuration and the degrading subunits (11.ij) have a length ( Lsij) are aligned along the corresponding beam axis (Xi) in decreasing order. The degrading subunits (11.ij) are preferably arranged coaxially and with the orifice with the longest length (Lsi3) located in the central position. The degrading subunits (11.ij) can also be arranged in other configurations, eg non-concentric configurations and with the orifice of longest length (Li3) not necessarily central.

In embodiments in which the degrading subunits (11.ij) are arranged concentrically, of the subunit base areas (Aij) of each degrading subunit (11.ij), the deepest orifice (11.i3) has a circular geometry except for the base area (Ai3) of the subunit. As a result, the subunit base area (Aij) of a given degrading subunit (11.ij) is the sum of the cross-sectional area (Axij) of the given degrading unit (11.ij) and the given degrading The cross-sectional area of the degrading subunit (11. ) is the cross-sectional area of the orifice perpendicular to the corresponding beam axis (Xij) contained within the perimeter of the cross-section of the degrading subunit (11.ij).

In alternative embodiments shown in FIGS. 4(f)-4(j), the degrading subunits may be arranged in a side-by-side configuration. In this embodiment, the degrading subunits are two degrading subunits (it is easy to imagine a corresponding design with orifices) as shown for the pins in FIGS. 7(e) and 7(g). Arranged side by side within the base area (Abi) with either no space between units or space between two degrading subunits as shown in adjacent FIGS. 4(f) and 4(g) be done.

In further alternative embodiments, the degrading subunits may be arranged in a mixture of both serial and parallel configurations. In this configuration shown for the pins in FIGS. 7(h) and 7(i) (it is easy to imagine a corresponding design with orifices), three or more degrading subunits (11.ij) Arranged both in series and in parallel, one or more structures formed by two or more degrading subunits aligned in series along corresponding beam axes (Xi), optionally one or a plurality of individual degrading subunits arranged side by side within a base area (Abi).

This embodiment is particularly easy to manufacture by machining or etching the blocks forming the support base (11b) or forming them by three-dimensional printing techniques. Given that the maximum fluence of the beam (100.i) is on the beam axis (Xi), the manufacturing error of the degrading subunit (11.ij) that intersects the beam axis (Xi) at the maximum of the Gaussian distribution of fluences is more important than at peripheral locations. Using orifices rather than pins has the advantage that the weight assigned to the Bragg peak matches the fluence of the spot. In fact, Bragg peaks with greater range are usually Bragg peaks with greater weight (ωij) in the treatment plan. Therefore, the corresponding subunit (ie, the subunit with the shortest length Li) can be placed at the position of highest fluence (ie, center) of the beam. In addition, the subunits with the longest lengths Li usually correspond to Bragg peaks with low weights (shortest range Bragg peaks) and thus have small cross-sections. Therefore, subunits are conveniently placed in the region of the spot with the lowest fluence. Forming an orifice to tight tolerances is easier than forming a thin pin of the required length (Lij) to the same tolerances to achieve the desired effect. Offsetting the degrading subunits with the longest length (Lij) can also help reduce the weight of small deviations in manufacturing.

For clarity, FIGS. 4(a)-4(e) show an energy degrading unit (11.i) formed of three degrading subunits (11.ij) and FIG. 7(b ) denotes an energy degrading unit (11.i) formed of only two degrading subunits (11.ij). It is clear that the number of degrading subunits (N) can actually be higher in order to obtain a smoother SOBP plateau. Figures 6(a)-6(c) show similar energy degrading units (11.i) with 3, 6 and an "infinite number" of degrading subunits (11.ij), with infinite In the case of numbers, truncated triangular pyramidal orifices are formed. All orifices in FIGS. 6(a)-6(c) are orifices of length (Lsi3) with opening area (Axi1) and bottom area (Axi3) (see Figure 4(a) to 4(e)).

In FIGS. 4(c)-4(e), each degrading subunit is shown separately, the whole forming a generalized hollow cylinder, which are fitted together to form the digrading unit of FIG. 4(b). Forms a grading subunit. In practice, the degrading subunit (11.ij) of FIG. 4(b) is machined or etched into the support base (11b) to form orifices, or ridges with corresponding orifices are formed by three-dimensional printing techniques. It can be manufactured by forming a filter.

）ように構成される。 If the degrading unit (11.i) is a pin In an alternative embodiment shown in FIGS. 5(a)-5(e), 7(a), 7(e) and 7(f) , energy degrading units (11.i) arranged side by side according to an array of spots (Si) and supported on a support base (11b) of thickness (Bi) measured along the beam axis (Xi) It is in the form of a pin. Each pin extends from the support base along a corresponding beam axis (Xi). Each energy degrading unit (11.i) has a generalized cylindrical geometry of cross-sectional area (Axij) and a length such that Lij = Bi + Lsij from the support base along the corresponding beam axis (Xi) (Lsij) is formed by one or more degrading subunits (11.ij, 11.i3, 11.i2, 11.i1). so that the degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) are within a diameter slightly greater than or equal to the diameter (D100) of the beam (100.i), and The sum of the subunit base areas (Aij) equals the base area (Abi) (i.e.

) is configured as

In the preferred embodiment shown in FIGS. 5(a)-5(e) and 7(a), the degrading subunits (11.ij) are arranged in series. In this structure, the degrading subunits are aligned in order of decreasing length (Lsij) along the corresponding beam axis (Xi). The degrading subunits are preferably arranged coaxially and with the pin having the longest length (Lsi1) located in the central position.

In embodiments in which the degrading subunits (11.ij) are arranged concentrically, the base area (Aij) of the subunits of a given degrading subunit (11.ij) is the same as that of a given degrading unit (11.ij). 11.ij) and the cross-sectional area of the degrading unit circumscribed within the given degrading unit (Axi(j−1)) (Axij−Axi(j −1)). In other words, for a finite number N of degrading subunits (11.ij), the pins are in the form of stepped pyramids (see FIGS. 4(b)-4(e)). The area (Aij) of a given degrading subunit (11.ij) determines the next degrading subunit (11.i(j+1)) of smaller dimension than the given degrading subunit (11.ij). The area of the stair tread (or flange) formed by a given enclosing degrading subunit (11.ij).

In alternative embodiments shown in FIGS. 5(f)-5(j), 7(e) and 7(g), the degrading subunits may be arranged in a side-by-side configuration. In this embodiment, the degrading subunits are shown in FIGS. 7(e) and 7(g) with no space between the two degrading subunits or adjacent FIGS. 5(f) and 5(g). Arranged side by side within the base area (Abi) either with a space between the two degrading subunits as shown in g). For example, in the embodiments shown in FIGS. 7(e) and 7(g), the degrading subunits are arranged side by side, with the longest degrading subunits offset with respect to the corresponding beam axis (Xi). is preferred. In this way, the longest degrading unit faces a portion of the beam (100.i) with less weight, thus allowing the cross-sectional area (Aij) to be increased, thereby increasing the energy degrading unit (11.i). The production of i) is facilitated. The same configuration can be applied to the energy degrading units (11.i) in the form of orifices discussed above.

In further alternative embodiments, three or more degrading subunits may be arranged in a mixture of both serial and parallel configurations. In this configuration, shown in FIGS. 7(h) and 7(i), three or more degrading subunits (11.ij) are arranged both in series and in parallel, one or more structures corresponding formed by two or more degrading subunits aligned in series along the beam axis (Xi), optionally with one or more individual degrading subunits arranged side by side within a base area (Abi) be done.

For clarity, FIGS. 5(a)-5(e) and 7(f) show an energy degrading unit (11.i) formed of three degrading subunits (11.ij) 7(a) and 7(e) show an energy degrading unit (11.i) formed of only two degrading subunits (11.ij). It is clear that the number of degrading subunits (N) can actually be higher in order to obtain a smoother SOBP plateau. Energy degrading units (11.i) in the form of pins, as shown in FIGS. It can comprise any number of subunits (11.ij), etc., forming a truncated cone in the case of an infinite number (see FIG. 6(e)). Regardless of the number N of degrading subunits (11.ij), all pins are pins of length (Lsi3) with base area (Ai1) and tip area (Ai3) (for the meaning of the symbols 5(a) to 5(e)).

In FIGS. 5(c)-5(e) each degrading sub-unit is shown separately and in its entirety when they are fitted together to form the degrading sub-unit of FIG. 5(b). In practice, the degrading subunit (11.ij) of FIG. 5(b) is preferably produced by machining, etching or three-dimensional printing a monolithic energy degrading unit (11.i) with a support base (11b). or by machining, etching or three-dimensional printing each degrading subunit (11.ij) individually and assembling them to form the energy degrading unit (and support base (11b)). obtain. Most preferably, the entire ridge filter is produced monolithically (ie, no assembly steps are required).

Degrading units (11.i) made of different materials
In a third embodiment shown in FIGS. 7(c) and 7(d), it is possible to combine the above embodiments of the energy degrading unit in the form of cavities or pins discussed above with the third embodiment. at least the first degrading subunit (11.11) of the first energy degrading unit (11.1) may be the first energy degrading unit (11.1) or the second degrading unit ( 11.2) made of a first material different from the second material of the second degrading subunit (11.ij). The first material has a length of the first degrading subunit (11.11) (L11= W11/Wu) has a different value of water equivalent thickness (Wu) of the subunits per unit length than the second material in order to change, preferably decrease, the value of W11/Wu).

FIG. 7(c) shows an embodiment comprising a first degrading subunit (11.i1) and a second degrading subunit (11.i2) arranged concentrically. The second degrading subunit (11.i2) is enclosed within the annular first degrading subunit (11.i1). The first degrading subunit (11.i1) has a higher subunit water equivalent thickness (Wu) per unit length than the material forming the second degrading subunit (11.i2). Made from 1 material. It follows from this that for the same length (Li1=Li2) measured along the beam axis (Xi), the first degrading subunit (11.i1) absorbs more energy from the beam. , shifts the Bragg peak to cells of smaller cell water equivalent thickness (di1<di2) lower than the water equivalent thickness (di2) of the cell across the second degrading subunit (11.i2).

Figure 7(d) shows a similar configuration, but the first degrading subunit (11.i1) is a unit longer than the second material from which the second degrading subunit (11.i2) is made. It is made of a first material with a high water equivalent thickness (Wu) value of the perimeter subunit and is centrally located surrounded by a second degrading subunit (11.i2). As a result, the depth (di1<di2) at which the Bragg peak of some beams occurs across the first degrading subunit (11.i1) located in the center of the energy degrading unit (11.i) is the beam Less than the rate across the second degrading subunit (11.i2) is the same as the length (Li1=Li2) measured along the axis (Xi). The degrading subunits (11.i1, 11.i2) in FIGS. 7(c) and 7(d) are arranged concentrically. It is clear that other configurations are possible, for example a side-by-side arrangement. Having the same length Li1=Li2 is also an optimized situation. Since it is not possible to continuously select materials over the entire range of subunit water equivalent thickness (Wu) values per unit length, the required cell water equivalent thickness (dij) can be obtained while maintaining the same length It is difficult to choose materials with (Lij). However, by changing the materials, the height difference between the degrading subunits can be reduced, resulting in a more compact and robust energy degrading unit (11.i).

This embodiment of combining different materials with different subunit water equivalent thicknesses (Wu) per unit length shortens the length (Lij) of the longest degrading subunit (11.ij) and shortens the length (Lij) of the shortest digrading subunit (11.ij). It can be applied to both cavity-like and pin-like energy degrading units (11.i) so as to lengthen the length of the grading subunits (11.ij) to obtain shorter ridge filters (11). , and eases production in terms of tolerances, but the most suitable dimensions for production can be chosen.

For example, the selection of materials for each degrading subunit includes keeping the length of the first degrading subunit (L11) within ±20% of the length of the second degrading subunit (Lij). can be the purpose. Preferably, the lengths (Lij) of all degrading subunits (11.ij) of the energy degrading unit (11.i) are the same within ±20% variation of the average length (Lm,ij) (ie, Lij=Lm, ij±20%∀j). In this way a compact ridge filter can be obtained.

Ridge Filter (11) and Particle Accelerator with Ridge Filter (11) As shown in Figure 3(c), the ridge filter (11) comprises a plurality of energy degrading units ( 11. i). The position of the individual energy degrading units (11.i) corresponds to the position of the corresponding spot (Si) and its orientation is parallel to the corresponding beam axis (Xi).

In FIGS. 1(a), 1(b), 3(a) and 3(e) all beam axes (Xi) are shown parallel to each other. This is not exactly correct because all beam axes (Xi) start from the same point in the center of the scanning electromagnet at the nozzle and are diverted to scan all the spots (Si) that characterize the treatment volume (V). . This is illustrated in FIGS. 3(b), 3(d) and 3(f), where the deflection angles are exaggerated for clarity. The aperture angles of the cones enclosing all beam axes (Xi) depend on the distance between the scanning magnet and the treatment volume (V) and the size of the treatment volume (V). FIG. 3(b) shows a view of the illumination system corresponding to the view of FIG. 3(a), with the beam axis deviated from parallel to account for beam scanning effects. In FIG. 3(b), the opening angle is exaggerated. Figure 3(c) shows the corresponding ridge filter (11) with pins protruding from the support base (11b) and out of parallel with each other. Figure 3(d) shows two energy degrading units formed by two corresponding orifices in the support base (11b). Again, the angles of the openings are exaggerated for clarity.

In practice, the aperture angle is generally within ±5°, preferably within ±3°, more preferably within ±1° from the illumination axis (X). For this reason, although not strictly correct, representing the beam axes (Xi) parallel to each other in the drawings is a simplification of an acceptable reality.

Figures 3(e) and 3(f) show similar cubic elements of a treatment volume (V) containing several sub-volumes (Vi). The sub-volumes (V1, V4 and V5) are shown in cutaway side view showing the positions of the corresponding cells (Cij, i=1, 4 and 5, j=1-4). In FIG. 3(e) the sub-volumes (Vi) extend (substantially) parallel to each other and (substantially) parallel to the irradiation axis (X), and in FIG. (Xi) (again, the opening angle is exaggerated for clarity).

Degrading subunits (11.i1) with the longest length (Li1) measured along the corresponding beam axis (Xi) add more energy to the beam (100.i) than shorter degrading subunits. Absorb. Thus, the longest degrading subunit (11.i1) determines the water-equivalent thickness (di1) of the shortest cell that defines the position of the nearest Bragg peak of the patient's skin (3s). As the length (Lij) of the degrading subunit (11.ij) decreases, the shortest length (LiN ), the water equivalent thickness (dij) of the corresponding cell increases. The superposition of all Bragg peaks forms the SOBP that must follow the treatment regimen (see FIGS. 4(a)-4(e) and 5(a)-5(e)). The length (Lij) of each degrading subunit (11.ij) can be readily determined as Lij = Wij/Wu = (W0-dij)/Wu as discussed above (Fig. 2( b)).

The area (Aij) of each degrading subunit (11.ij) is the number of charged particles required to impart a given dose (Dij) to the corresponding cell at the water equivalent thickness (dij) of the respective cell. must be dimensioned to provide Equation (1) is used to determine the value of the area (Aij) of the degrading subunit (11.ij).

In equation (1), the normalized beam weight (ωij) is equal to the normalized value of the integral of the beam fluence (F(y,z)) over the dimensioned area (Aij). The area (Aij) defines a boundary along which the integral of the numerator of equation (1) is computed so that the area (Aij) can be determined for each degrading subunit (11.ij) . As discussed above, a preferred arrangement of the individual degrading subunits (11.ij) is to form the corresponding energy degrading units (11.i). (see FIGS. 4(a)-4(e) and 5(a)-5(e)). In this tandem arrangement, the area (Aij) of the first degrading subunit (11.ij) is the coaxially inscribed degrading subunit (11.i(j+1) ) has an annular geometry forming an annular step around the perimeter. 4(f)-4(j), 5(h)-5(j)), and 7(e) and 7(g), the degrading subunit The area (Aij) in (11.ij) is the area at the base of each degrading subunit.

In the case of a dense array of spots (Si), the spots (Si) are not more than 1.8 times the standard deviation (σ) of the fluence (Fi (y, z)) of the beam (100.i), preferably 1.5 The fluence of beams separated from each other by a distance (ds) less than or equal to double and passing through the base area (Abi) is constant over all values of the plane (Y, Z) j defining the inscribed boundary of the volume (V) is approximated as This configuration greatly simplifies solving the integral in the numerator of equation (1).

であるように近似され、ここで、（ｙｉ，ｚｉ）は、（Ｙ，Ｚ）平面におけるスポット（Ｓｉ）のフルエンスの最大値（Ａｉ）の位置の座標であり、円形スポットの場合、σ_ｙ＝σ_ｚ＝σである。式（１）の分子における積分を解くことは、スポット（Ｓｉ）の配列が密である場合（すなわちｄｓ＜１．８σ又は＜１．５σ）ほど簡単ではないが、少なくとも数値的に解くことができる。スポットが円形であり、σ_ｙ＝σ_ｚ＝σである場合、式（１）を解くことは簡単になる。 If the array of spots (Si) is relatively sparse, the spots should be more than 1.2 times the standard deviation (σ) of the fluence (Fi(y,z)) of the beam (100.i) (i.e. ds>1 .2σ), preferably more than 1.5 times the distance (ds) from each other, and the fluence (Fi(y,z)) of the beams (100.i) passing through the base area (Abi) has a Gaussian distribution

where (yi,zi) are the coordinates of the location of the maximum fluence (Ai) of the spot (Si) in the (Y,Z) plane, and for a circular spot, σ _y = σ _z = σ. Solving the integral in the numerator of Eq. (1) is not as straightforward as when the array of spots (Si) is dense (i.e. ds < 1.8σ or <1.5σ), but at least it can be solved numerically can. If the spot is circular and σ _y =σ _z =σ then solving equation (1) becomes straightforward.

Conclusion The method proposed here to design and dimension a ridge filter (11) for single-layer PBS painting of treatment volume (V) is simple, reliable and reproducible. . The design of energy degrading units (11.i) in the form of cavities is more robust to manufacturing tolerances than pins formed by concentric degrading subunits (11.ij), which allows for This is because the central degrading subunit (11.i1) is the longest and thinnest of all the energy degrading units (11.i) at the same time, making the precise manufacture of the pins more complex. Configurations other than concentric are also possible, such as stacking, to alleviate this problem. Using a material with a high subunit water equivalent thickness (Wu) per unit length for the longest length (Lij) degrading subunit (11.ij) also accurately fabricates elongated pins. This is a solution for reducing the problem of

Starting from a treatment plan, an array of spots (Si) is defined as above, the treatment volume (V) is divided into sub-volumes (Vi) (one per spot), and sub-volumes (Vi) are It can be divided into N cells (Cij). The dose (Dij) to be delivered to the cell (Cij) is determined based on the treatment plan.

The ridge filter is designed with as many energy degrading units (11.i) as there are spots (Si). Each energy degrading unit (11.i) is formed by N degrading subunits (11.ij) with length (Lij) and area (Aij).

The length (Lij) of each degrading subunit (11.ij) is calculated as the ratio of the water equivalent thickness (Wij) of the desired subunit to the water equivalent thickness (Wu) of the subunit per unit length. (ie Lij=Wij/Wu). The subunit water equivalent thickness is defined as Wij=W0-dij, where W0 is the maximum beam range and dij is the desired position of the Bragg peak at the center of the corresponding cell (Cij). The length (Lij) must take into account the thickness (Bi) of the supporting blocks (11b) supporting all the energy degrading units (11.i).

The area (Aij) of each degrading subunit (11.ij) is obtained by finding the area (Aij) over which the integral in the numerator of equation (1) is computed. This operation can be performed numerically.

The individual energy degrading units (11.i) are arranged on support blocks (11b) so as to extend coaxially along their respective beam axes (Xi). Ridge filters may be manufactured by machining blocks, attaching individual pins to support blocks (11b), three-dimensional printing techniques, and the like. The ridge filter (11) thus manufactured is placed between the exit of the charged particle accelerator and the treatment volume (V) such that each sub-volume (Vi) is coaxial with the corresponding beam axis (Xi). can be placed in Irradiation can begin with a single layer PBS painting.

A ridge filter (11) designed by the method of the present invention can cover the entire treatment volume with a single painting layer, thereby increasing the scanning time required to deliver the dose (Dij) to each slice (Tj) A treatment plan that includes FLASH irradiation of at least a portion of the treatment volume (V) that needs to be dosed (Dij) to the cell (Cij) at a very high dose delivery rate (HDR) by PBS, since the is significantly shortened particularly suitable for

3s skin 11 ridge filter 11 . i energy degrading unit 11 . ij degrading subunit 100 . i beam Abi base area (Abi) of degrading unit (11.i)
Aij degrading subunit 11 . ij base area Axij cross-sectional area of the energy degrading unit (11.i) at the depth of the degrading subunit (11.ij) Bi thickness of the support block along the irradiation axis (X) Cij cell d0 shortest water equivalent Thickness d1 farthest water equivalent thickness dij water equivalent thickness of the cell Dij dose F(y,z) beam fluence Lij length of degrading subunit (11.ij) along beam axis (Xi) Lsij = Bi−Lij . energy degrading unit in the form of a cavity Si spot Tj slice V treatment volume Vi partial volume W0 maximum beam range Wu water equivalent thickness of subunit per unit length X irradiation axis Xi beam axis X,Y,Z coordinate system (Y , Z) beam 100 . weight of i

Claims (10)

A single painting defining the entire treatment volume (V) at a specific location within the treatment volume (V) of tissue containing tumor cells (3t) using a beam of accelerated particles (100.i). A ridge filter of a charged particle accelerator, preferably a proton accelerator, to deliver a specific dose (Dij) by pencil beam scanning (PBS) spot by spot (Si) according to a predetermined treatment plan (TP) in the layer. In the method of design, said beam (100.i) is substantially parallel to the axis of irradiation (X) and parallel to said axis of irradiation (X) by an angle comprised within ±5°, preferably within ±3°. extending along a corresponding beam axis (Xi) diverging from said tissue and characterized by a maximum beam range (W0) defined as the water equivalent distance at which said beam no longer propagates through said tissue, said method comprising:
Define an area (Aj) across the upstream plane (Y,Z)j of N slices (Tj=T1-TN) of thickness (dxj) to inscribe the treatment volume (V) defining, wherein said plane (Y,Z)j is perpendicular to said irradiation axis (X) and the shortest water equivalent thickness (d0) and the longest water equivalent thickness (d1) for the patient's skin are said defined respectively as the boundary point closest to the skin and the boundary point furthest from the skin, measured along the illumination axis (X);
- defining an array of sub-volumes (Vi), each sub-volume parallel to the corresponding beam axis (Xi) from the skin of the patient to the corresponding furthest water equivalent thickness (dl); Extending, the projection of the array of sub-volumes (Vi) onto a plane (Y,Z) perpendicular to the illumination axis (X) is the projection of the volume (V) onto the plane (Y,Z). defining an array of spots (Si) covering the whole area,
- for each slice (Tj) of said N slices (T1 to TN) contained within a partial volume (Vi), defined as a portion of said partial volume (Vi) contained within said corresponding slice (Tj) defining a cell (Cij) that
- for each cell (Cij) of said given partial volume (Vi), determine the water equivalent thickness (dij) of the cell from said skin (3s) to the geometric center of said cell (Cij); Determining the beam weights (ωij) required to impart said particular dose (Dij) to said cell (Cij) according to TP, said beam weights (ωij) being the water equivalent thickness of said cell (dij ), a step proportional to the number of charged particles in
- designing said ridge filter (11) comprising a set of energy degrading units (11.i), each energy degrading unit (11.ij) having said specific dose (Dij) of According to said TP, said corresponding beam axis (Xi) and partial volume ( Vi) is configured to reduce the initial energy (E0) of a beam (100.i) of corresponding charged particles of beam diameter (D100.i) to a reduced energy (Eij), Said energy degrading unit (11.i) of a given partial volume (Vi) is:
o For each cell (Cij) of said partial volume (Vi), the base of the area (Aij) perpendicular to said corresponding beam axis (Xi) and the length (Lij) parallel to said corresponding beam axis (Xi) dimensioning a degrading subunit (11.ij) having a generalized cylindrical geometry with the generatrix of , said degrading subunit along said corresponding beam axis (Xi) of subunits per unit length Made of a material having a water equivalent thickness (Wu), said length (Lij) is such that said degrading subunit (11.i) is equal to said water equivalent thickness (Wu) of said subunit per unit length and said is determined to have the water equivalent thickness of the subunit (Wij = Wu x Lij) equal to the product of the length (Lij) and the water equivalent thickness of the subunit (Wij) and the water equivalent thickness of the cell (dij) is equal to the maximum beam range (W0) (i.e., W0 = Wij + dij), and o the area (Aij) of the degrading subunit (11.ij) is the normalized beam weight (ωij /Σ _j ω _ij ) for the integral of the fluence (F(y,z)) over the base area (Aij) of said subunit over the same integral over the base area (Abi) of said degrading unit (11.i) determined by equating to the ratio,

where the fluence F(y,z) is the number of charges per unit area of the beam (100.i) at the beam position (y,z), and the base area (Abi) is the equal to the sum of the areas (Aij) of the subunits (i.e. Abi = Σ _j Aij); designed to combine said N degrading subunits (11.ij) to obtain said energy degrading unit (11.i) designed to degrade energy;
- designing said energy degrading units (11.i) corresponding to all remaining partial volumes (Vi) as defined above, wherein the expression "water equivalent thickness" (=WET) is defined as the thickness of water that causes the same energy degradation of the particle beam as a given thickness of one or more materials traversed by the particle beam. 2. The method of claim 1, wherein the specific dose (Dij) is delivered according to the treatment plan at a very high dose delivery rate (HDR) to at least the selected specific location within the tissue volume (V). and HDR is defined as a dose delivery rate of HDR≧1 Gy/s. 3. A method according to claim 1 or 2, wherein the spots (Si) of the array of spots are a measure of the fluence (Fi(y,z)) of the beam (100.i) in one single spot. Said beams (100.i ) is approximated to be constant over all values of the plane (Y,Z) j defining the boundary inscribed in the volume (V). A method characterized. 3. A method according to claim 1 or 2, wherein the spots (Si) of the array of spots have a standard deviation of the fluence (Fi(y,z)) of the beam (100.i) in a single spot ( said beams (100.i) separated from each other by a distance (ds) greater than 1.2 times σ) (i.e. ds>1.2σ), preferably greater than 1.5 times and passing through said base area (Abi) The fluence (Fi(y,z)) of is Gaussian distributed

where (yi,zi) are the coordinates of the position of the maximum fluence (Ai) of the spot (Si) in the (Y,Z) plane, and , then σ _y =σ _z =σ. A method according to any one of claims 1 to 4,
- said energy degrading units (11.i) were arranged side by side according to the arrangement of said spots (Si) on a supporting base (11b) of thickness (Bi) measured along said beam axis (Xi) in the form of orifices, each extending from an opening opening into the surface of said support base (11b) and penetrating to a given depth measured along said corresponding beam axis (Xi); ,
each energy degrading unit (11.i):
o have a generalized cylindrical geometry of cross-sectional area (Ai) and from said opening of said support block (11b) along said corresponding beam axis (Xi) such that Lij=Bi-Lsij formed by one or more degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) in the form of orifices extending across (Lsij);
o A method characterized in that said degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) are located within said base area (Abi). A method according to claim 5, wherein the energy degrading unit (11.i) comprises at least two subunits (11.ij) arranged within said base area (Abi) in one of the following configurations: ,
・In series structure,
o the degrading subunits are arranged along the corresponding beam axis (Xi) in order of decreasing length (Lsij), preferably coaxially, and centered with the orifice having the longest length (Lsi3); are aligned so that the
o The subunit base area (Aij) of a given degrading subunit (11.ij) is the sum of the cross-sectional area (Axij) of the given degrading unit (11.ij) and the given digrading unit (11.ij). equal to the difference in cross-sectional area (Axij−Axi(j+1)) between the cross-sectional area of said degrading unit circumscribed within the grading unit (Axi(j+1));
In a parallel structure, the degrading subunits are within the base area (Abi) either with no space between two degrading subunits or with space between two adjacent degrading subunits. are placed side by side in the
- in a mixed structure of both parallel and serial, three or more degrading subunits (11. ) and optionally one or more individual degrading subunits are arranged side by side within said base area (Abi) A method characterized by: A method according to any one of claims 1 to 4,
- said energy degrading units (11.i) are arranged side by side according to said array of spots (Si) and on a supporting base (11b) of thickness (Bi) measured along said beam axis (Xi); each pin extending from said support base along said corresponding beam axis (Xi);
each energy degrading unit (11.i):
o one having a generalized cylindrical geometry of cross-sectional area (Aij) and extending from the support base along the corresponding beam axis (Xi) for a length (Lsij) such that Lij=Bi−Lsij or formed by multiple degrading subunits (11.ij, 11.i3, 11.i2, 11.i1),
o A method characterized in that said degrading subunits (11.ij, 11.i3, 11.i2, 11.i1) are located within said base area (Abi). A method according to claim 7, wherein the energy degrading unit (11.i) comprises at least two subunits (11.ij) arranged within said base area (Abi) in one of the following configurations: ,
・In series structure,
o The degrading subunits are preferably coaxial, in order of decreasing length (Lsij), along the corresponding beam axis (Xi), and the pin having the longest length (Lsi1) is centrally positioned are aligned so that the
o The subunit base area (Aij) of a given degrading subunit (11.ij) is the sum of the cross-sectional area (Axij) of the given degrading unit (11.ij) and the given digrading unit (11.ij). is equal to the difference in cross-sectional area (Axij-Axi(j-1)) between the cross-sectional area (Axi(j-1)) of said degrading unit circumscribed within the grading unit;
- in a mixed structure of both parallel and serial, three or more degrading subunits (11. ) and optionally one or more individual degrading subunits are arranged side by side within said base area (Abi) A method characterized by: 9. A method according to any one of claims 5 to 8, wherein at least a first degrading subunit (11.11) of a first energy degrading unit (11.1) comprises: made of a first material different from the second material of the second degrading subunit (11.ij) of the grading unit (11.1) or the second energy degrading unit (11.2), said first One material has a length (L11 =W11/Wu), which is different from that of the second material so as to change, preferably decrease, the value of the water equivalent thickness (Wu) of the subunit per unit length Method. A method according to claim 9, wherein said length (L11) of said first degrading subunit (11.11) is ±20% of said length (Lij) of said second degrading subunit. and preferably said length (Lij) of all said degrading subunits (11.ij) of an energy degrading unit (11.i) is ±20 of the average length (Lm,ij) A method characterized by having the same length (Lij) within % variation (ie, Lij=Lm, ij±20%∀j).

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